1. Field of the Invention
The present invention relates to a capacitive micromachined ultrasonic transducer (cMUT).
2. Description of the Related Art
An ultrasonic diagnosis method in which an ultrasound is transmitted toward an internal wall of a body cavity and a state of the interior of a human body is diagnosed by imaging it with an echo signal of the ultrasound is popular. One type of equipment used for the ultrasonic diagnosis method is an ultrasonic endoscope (e.g., refer to reference Laid-Open Japanese Patent Application Publication No. 2004-350701).
The ultrasonic endoscope is equipped with an ultrasonic probe at the head of an insertion tube which is to be inserted into a body cavity. The ultrasonic probe is for converting an electric signal into an ultrasound, transmitting it to a body cavity and converting an ultrasound into an electric signal by receiving the ultrasound reflected from the body tissue.
While a conventional ultrasonic probe uses the ceramic lead zirconate titanate (PZT) as a piezoelectric element for converting an electric signal into an ultrasound, recently receiving attention is a Capacitive Micromachined Ultrasonic Transducer (simply noted as “cMUT” hereinafter) which is produced using a silicon micromaching process. This is one of devices generically called a Micro Electro-Mechanical System (MEMS).
The cMUT is collectively featured with a plurality of cMUT cells with the electric terminal of each cMUT cell being parallelly connected so as to constitute a unit of the cMUT element which is a unit for signal controlling. Furthermore, a large number of the cMUT elements are arrayed, thus constituting a cMUT.